1. Field of the Invention
The present disclosure relates to drip irrigation emitters that are used to control the provision of liquid to plants.
2. Background of the Invention
Such drip emitters are normally coupled to an irrigation pipe and are provided with an inlet, an outlet and a flow-restricting path therebetween. Liquid passing from the pipe via the inlet into the emitter; traverses through the flow-restricting path to be released at the outlet of the emitter at a relatively low discharge pressure generally equal to about zero.
In some drip emitters a flexible diaphragm is provided to control liquid flow so that it is substantially independent of inlet pressure. The diaphragm is usually located between the inlet and the outlet and is responsive to pressure of the entering liquid so that as the pressure of the entering liquid increases, the diaphragm undergoes distortion that operates to increase resistance to liquid flow through the dripper.
U.S. Pat. No. 6,302,338, the disclosure of which is incorporated herein by reference, describes a one-way valve in the form of a cap which permits water flow from an interior of a water supply tube towards a water discharge opening, but blocks water flow in the reverse direction. When the water pressure within the tube is above a predetermined minimum pressure, the water bearing against the inner side of the valve deforms the valve thereby permitting water flow past the valve. The water pressure at the outer side of the valve, which exhibits a slight drop in pressure in relation to the inner side of the valve, flows onwards via a pressure reducing labyrinth to be discharged at a water pressure substantially equal to zero via an opening in the water supply tube.
In emitters such as the one described above; when water passes the valve into the emitter, the water pressure immediately after the valve bears against the valve to restrict the flow of water that passes the valve.
U.S. Pat. No. 5,111,996, the disclosure of which is incorporated herein by reference, describes an emitter coupled to a conduit that has valves that are used to control the length of a fluid-flow-limiting passageway, such as a labyrinth. The emitter's labyrinth is divided into sections and a series of valves selectively force the fluid entering the labyrinth to flow through additional sections of the labyrinth as the pressure in the conduit rises.